While the rapid development of light emitting diode (LED) in the electronic industry enables constantly increased density of circuits on a circuit board, the heat accumulated on the circuit board in use also increases and can not be easily removed. Generally speaking, in the event the heat energy produced by LEDs when they emit light is not properly dissipated, the LEDs would have excessively high junction temperature to adversely affect the service life, luminous efficiency and stability thereof.
To obtain upgraded LED luminous efficiency and service life, one of the currently most important tasks is to solve the heat dissipation problem of the LED products. Since the LED industry aims to develop high-power, high-brightness and small-sized LED products, it has also become an important trend in future development of LED products to provide a heat dissipation LED substrate having high thermal conductivity and precision dimensions. Currently, the main trends for developing upgraded LED luminous efficiency include the use of aluminum nitride substrate in place of aluminum oxide substrate and the use of eutectic process or flip chip process in place of gold wire bonding process to electrically connect an LED die to a substrate. In the above two LED developing trends, extremely strict requirements have been set for the highly accurate alignment of circuits on the heat dissipation substrate, and the heat dissipation substrate must have high heat dissipation ability, small dimensions and good adhesion to metal traces.
The technique for fabricating printed circuit board (PCB) has become highly mature in recent years. In the early stage, most of the system circuit boards for LED products are PCBs. However, PCBs have limited heat dissipation ability and therefore could not be used with high-power LED products, whose demand has largely increased in recent years. To solve the high-power LED's problem in heat dissipation, some manufacturers have adopted a type of metal core printed circuit board (MCPCB) that has high thermal conductivity. That is, good heat dissipation ability of metal materials is utilized to achieve the purpose of dissipating heat produced by high-power LED products. However, due to the constantly increased demand for high LED brightness and performance, the improved system circuit board capable of effectively dissipating the heat produced by the LED chips into ambient air is now not good enough for use because the heat produced by the LED dies can not be effectively transferred from the dies to the system circuit board for dissipation.
The currently available electrically insulating materials include ceramic materials and high thermal conduction plastic materials. Ceramic materials have been utilized by human for thousands of years. The ceramic materials prepared with modern technology have the advantages of good insulating ability, high heat-transfer rate, high infrared radiation rate, low thermal expansion coefficient and the like, and have gradually become the new materials for LED lighting. Presently, ceramic materials are mainly used as heat sink materials for LED chip packaging, circuit board materials and radiator materials for lighting products. The high thermal conductivity plastic materials have excellent electrical insulating ability and low density but are expensive and accordingly have low utilization rate. Nevertheless, the high thermal conductivity plastic materials are also found in the heat dissipation material market.
Currently, there are four types of popular ceramic heat dissipation substrates, namely, high-temperature co-fired ceramic (HTCC) multilayer substrate, low-temperature co-fired ceramic (LTCC) multilayer substrate, direct bonded copper (DBC) substrate, and direct plated copper (DPC) substrate. HTCC is a technology developed in an earlier stage. HTCC requires a relatively high sintering temperature. Therefore, only limited materials can be selected for use as electrodes in HTCC technology, and the manufacturing cost thereof is relatively high. These disadvantageous factors bring to the development of LTCC, which has a lower co-firing temperature of around 850° C. compared to HTCC. However, with LTCC, it is uneasy to control the product's size accuracy and strength. As to DBC and DPC, they are specialized technology developed and becoming mature only in recent years, and allow mass production of heat dissipation substrates. DBC uses high temperature to bond a copper sheet to an aluminum oxide tile. The bottleneck in DBC is the micropores that exist between the aluminum oxide tile and the copper sheet and could not be easily removed to thereby form a considerably big challenge in the mass productivity and the yield rate of products. The DPC utilizes the technique of direct copper plating to deposit copper on an aluminum oxide substrate. This process combines material and thin film technology with it to create a product that has become the most popular ceramic heat dissipation substrate in recent years. However, DPC requires high material control and technology integration, which forms a high technical threshold for manufacturers to enter the DPC industry and stably produce ceramic heat dissipation substrates.
Therefore, it is necessary to provide a manufacturing method for solving the aforesaid technological problems.